In OFDM (Orthogonal Frequency-Division Multiplexing) communication, an input signal is modulated with subcarriers, and the modulated input signal is subjected to an IFFT (Inverse Fast Fourier Transformation) to generate a baseband signal. When the number of subcarriers increases to increase the FFT (Fast Fourier Transformation) size, therefore, a baseband signal with a high peak is generated, increasing the PAPR (Peak-to-Average Power Ratio). The increase in the PAPR needs an amplifier having a wide range of linearity to transfer a signal without distortion. To meet the requirement, techniques of reducing the PAPR are developed.
Unexamined Japanese Patent Application KOKAI Publication No. 2006-165781 discloses a technique of controlling the phase of a subcarrier modulation signal based on the optimal phase, calculated by a sequential decision procedure, prior to IFFT in order to reduce the PAPR.
The OFDM communication needs to cope with reducing the PAPR. The technique disclosed in Unexamined Japanese Patent Application KOKAI Publication No. 2006-165781 needs to control the phase, subcarrier by subcarrier, by repeatedly calculating the optimal phase to reduce the PAPR. In addition, the technique disclosed in Unexamined Japanese Patent Application KOKAI Publication No. 2006-165781 cannot control the degree of reduction in PAPR.